Vulnerability · Published Mar 26, 2026 · Assigned by GitHub_M

CVE-2026-33640Outline has a rate limit bypass that allows brute force of email login OTP

Critical 9.1

In plain English

A critical-severity security flaw in outline from outline. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities).

Severity (CVSS 4.0)9.1Critical

Exploit odds (30 days)0.5%top 58.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Outline is a service that allows for collaborative documentation. Outline implements an Email OTP login flow for users not associated with an Identity Provider. Starting in version 0.86.0 and prior to version 1.6.0, Outline does not invalidate OTP codes based on amount or frequency of invalid submissions, rather it relies on the rate limiter to restrict attempts. Consequently, identified bypasses in the rate limiter permit unrestricted OTP code submissions within the codes lifetime. This allows attackers to perform brute force attacks which enable account takeover. Version 1.6.0 fixes the issue.

Affected products (as reported)

Vendor	Product	Versions
outline	outline	>= 0.86.0, < 1.6.0

Weakness: CWE-307 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

References

https://github.com/outline/outline/security/advisories/GHSA-cwhc-53hw-qqx6 x_refsource_CONFIRM
https://github.com/outline/outline/releases/tag/v1.6.0 x_refsource_MISC